The teen suspect was arraigned Wednesday afternoon and charged as an adult, according to a CNN report. He has been charged with attempted homicide.

Another student, sophomore Nate Scimio, emerged as a hero in the rampage, in which the suspect stabbed and slashed seemingly at random, inuring 21 people, at least four seriously. The teen blocked the suspect from stabbing two sophomore girls, taking a stab wound in his arm in the process.

Scimio also reportedly set off a fire alarm during the Pittsburgh stabbing spree, a move credited with getting students out of the building and saving even more from being the stabbings.

“(Nate) took the stab right in his arm and saved my friend and me,” said sophomore Trinity McCool. “I’m pretty sure it was his instinct. He didn’t want anyone to get hurt. He told everybody to run away.”

Without Nate me and Lindsay would’ve been injured and there’s not enough words to describe how much of a hero he is

To let everyone know he was doing fine, Scimio later posted a Facebook “selfie” with the caption, “Chillin’ at Children’s,” a reference to Children’s Hospital where he was sent for treatment on his stabbing wound.

According to students and other witnesses, several students suffered stabbings before anyone knew what was going on — even the victims.

“They just felt pain and noticed they were bleeding,” said Dr. Timothy VanFleet, the emergency medicine chief at University of Pittsburgh Medical Center where some of the victims were taken.

One Franklin High School student, Mia Meixner, said that at first students simply thought a routine fight had broken out.

“I heard a big commotion like behind my back,” she told CNN. “And I turned around and I saw two kids on the ground. I saw the kid who was stabbing people get up and run away.”

She then saw another girl, a senior, “gushing blood down her arm.” After that, a “stampede” of panicked students followed.

“So then I just ran out of the school and tried to get out as soon as possible,” Meixner said.

She described seeing the stabbing suspect with “a look on his face that he was just crazy and he was just running around just stabbing whoever was in his way.”

Trinity McCool described the Pittsburgh school stabbing suspect as having “a look in his eyes. I was horrified.”

Meixner said that the suspect was “shy,” adding that she did not know him very well.

“He kept to himself a lot,” Meixner said. “He didn’t have that many friends that I know of, but I also don’t know of him getting bullied that much. I actually never heard of him getting bullied. He just was kind of shy and didn’t talk to many people.”

Four of the injured victims suffered wounds that a doctor described as “life threatening,” but Dr. Chris Kaufman of Forbes Regional Medical Center said all were expected to survive after emergency surgery.

The Pittsburgh school stabbing spree came to an end with the high school assistant principal tackled the suspect and a school security guard handcuffed him.